Preheat the oven to 200°C. Cut the sweet potato into large chunks. Melt 1 tbsp coconut oil and rub the sweet potato in the oil, then roast in the oven for 40 minutes until golden and cooked through.
Finely chop the onion. Heat the remaining coconut oil and add the chopped onion, a big pinch of salt and garlic. Sauté for 5 minutes, then add the coconut milk, roasted sweet potato and stock. Simmer for 10 minutes while you make the blackberry sauce.
Place the blackberries, basil, lemon juice, honey, a pinch of salt and balsamic in a pot. Bring to the boil then turn down to a simmer. Crush the blackberries with the back of a spoon and cook until the sauce reduces by half and thickens.
Blend the soup and top with the blackberry sauce and freshly chopped parsley.